The present invention is directed to a method for determining a connecting path in a communication network as well as to a corresponding switching equipment for use in communication networks, particularly in communication networks having hierarchically, complete determination of connecting paths.
As is known, communication networks are composed of a plurality of network or switching nodes that are connected to one another according to a specific network topology. Subscriber terminal equipment can be connected to some of these network nodes as user-specific line units of a communication network, whereas other network nodes serve only as transfer nodes, i.e. for forwarding communication information.
By way of example, FIG. 3a shows the structure of a binary-like communication network structure. According to FIG. 3a, the network shown by way of example comprises a total of ten network nodes K1-K10. A plurality of subscriber terminal equipment EG11-EG43 are respectively connected to the network nodes K1-K4 . These network nodes K1-K4 form the lowest hierarchy level of the communication network shown in FIG. 3a and are referred to as local network nodes. The local network nodes K1-K4 are connected to one another with corresponding connecting paths via the other network nodes K5-K10. According to the example shown in FIG. 3a, no subscriber terminal equipment are connected to the network nodes K5-K10, so that these network nodes serve only as transfer or switching nodes. The network nodes K5-K7 correspond to regional network nodes and serve the purpose of connecting the local network nodes K1 and K2, K2 and K3 or, respectively, K3 and K4 . Correspondingly, the network nodes K8 and K9 serve for connecting the regional network nodes K5 and K6 or, respectively, K6 and K7 and are referred to as super-regional network nodes. Finally, the node central K10 that connects the super-regional network nodes K8 and K9 to one another forms the highest hierarchy level of the communication system shown in FIG. 3a. When, for example, the subscriber EG42 is called from the subscriber terminal equipment EG12, a connecting path or, respectively, connecting route must be set up via the communication network proceeding from the local network node K1 to the local destination network node K4 of the called subscriber. There are thereby a number of connecting possibilities according to the communication network shown in FIG. 3a. One connection, for example, could lead via the network nodes K1-K5-K8-K10-K9-K7-K4. Another connecting possibility would be the connecting path via the [. . . ] K1-K5-K2-K6-K3-K7-K4, etc. The individual network nodes K1-K10 are formed by switching equipment whose jobs include determining the suitable connecting path from a calling terminal equipment to a called terminal equipment and setting up the corresponding connection.
Whereas FIG. 3a shows a tree-like communication network structure, FIG. 3b shows a cube-like communication network structure, whereby, in particular, respectively three network nodes K1-K3 form a network node group that is connected via corresponding connecting lines to a neighboring network node group that is likewise composed of three network nodes. Terminal equipment can be optionally connected to each of the network nodes shown in FIG. 3b or the corresponding network node can merely serve as a transfer node without terminal equipment connected thereto.
Due to the currently increasing need for digital communication networks with great bandwidths and high transmission rates, what is referred to as the ATM transmission principle (asynchronous transfer mode) has prevailed for data transmission in communication networks. According to this ATM transmission principle, the data to be transmitted are communicated in the form of what are referred to as ATM cells that are composed of a header and an information field. The header contains address or, control information of the corresponding ATM cell, whereas the information field comprises the actual payload information. The address information contained in the header are employed for the routing of the payload information within the communication network. The data transmission from one network node to another optically, i.e. via light waveguides.
In communication networks having hierarchically complete path determination, the network topology of the communication network is stored and, thus is known in the individual network nodes. Each network node or, the corresponding switching equipment of this network node is thus informed, for example, about how many and which other network nodes are present in the communication network, which connecting lines or, respectively, connecting paths exist between the individual network nodes and what transmission properties (for example, transmission capacities and transmission statusses) the corresponding connecting paths have. On principle, thus, every network node is in the position to determine a hierarchically complete connecting path to a desired destination node of the communication network. As a rule, the complete connecting path is defined by that network node to which the calling terminal equipment is connected (see the network nodes K1-K4 in FIG. 3a). After receiving the corresponding connection request (for example, to the terminal equipment EG42 shown in FIG. 3a), the originating node determines the entire path through the communication network up to the desired destination node on the basis of the information about the communication network available to it. After defining the suitable connecting path, the originating node or, the switching equipment thereof generates an information element in which the individual network nodes to be traversed along the defined connecting path are defined. Additionally, the connecting lines (ports) can also already be defined in the information element. Together with a pointer, this information element is communicated to the individual network nodes participating in the defined connecting path, whereby the pointer respectively points to the next network node to be approached. When, for example, a connection is requested from the terminal equipment EG12 shown in FIG. 3a to the terminal equipment EG42 and when the originating node K1has selected the route K1-K5-K2-K6-K3-K7-K7 [sic]-K4 for this connection, the individual network nodes K5, K2, K6K3, K7 and K4 to be approached are successively deposited in the corresponding information element in the form of a stack memory, whereby the pointer of the information element points first to the network node K5.
In order to keep the connection setup times relatively short, the connecting paths to every potential destination node of the communication network are determined in advance and stored in the individual network nodes. Due to the different quality demands (for example, bandwidth, delay, etc.) of a connection request or, of a connection inquiry and due to the increasing complexity of the communication networks, all possible connecting paths from an originating node to a destination node can usually not be calculated in advance and stored. First, there is thereby the risk of inadequate memory space; second, not all possible alternative paths are in fact usually made use of. Further, the time required for a connection setup lengthens if all possible alternative paths must be searched before the actual connection setup before the ultimately suited connecting path was capable of being found. When, on the other hand, all of the pre-calculated connecting paths fail to satisfy the demands of a connection request (for example, with respect to the bandwidth or transmission rate), a suitable connecting path must first be newly determined on the basis of the available network information. This can be a very time-intensive procedure dependent on the complexity of the communication network, as a result whereof the connection setup can be substantially delayed or, even jeopardized. As a compromise, only a specific plurality of standard connecting paths are therefore stored in each network node. For this purpose standard values are assumed for the individual connecting paths to each network node of the communication network with respect to the quality demands of the corresponding connection request, and, for example, only the respectively shortest path or paths to each potential destination node is/are calculated and stored. Given a pending connection request, all pre-calculated and stored connecting paths are then checked to see whether they meet the quality demands of the pending connection request. When one of the pre-calculated connecting paths meets the quality demands, this is employed for the connection setup to the requested destination node. When, however, none of the precalculated connecting paths meets the corresponding quality demands, a suitable alternative path to the requested destination node is determined on the basis of the stored network topology data and employed for the connection setup.
However, the above-described procedure has the disadvantage that, dependent on the pending connection request, it is still not possible to preclude relatively long connection setup times since only a relatively slight number of standard connecting paths is pre-calculated and stored, so that a suitable alternative path must potentially be determined first when none of these precalculated standard connecting paths can meet the quality demands of a requested connection, which can in part be very time-intensive dependent on the complexity of the communication network.